The present invention relates to batteries and more particularly to batteries having a built-in controller to extend the battery service run time.
Consumers use primary and rechargeable (secondary) batteries in portable electronic devices such as radios, compact disc players, cameras, cellular phones, electronic games, toys, pagers and computers devices. When the service run time of a primary battery is over, the battery is usually thrown away. The service run time of a typical primary battery generally only permits usage of between approximately 40 and 70% of the total battery storage capacity. Once that portion of the initial stored energy has been used, the battery generally cannot supply enough voltage to drive a typical electronic circuit. When the useful life of these batteries is spent, the consumers usually throw the batteries away even though the battery still contains between approximately 30 and 60% of its storage capacity. Thus, extending the service run time of a primary battery by allowing a safe deeper discharge will reduce waste by allowing the electronic devices to use more of the storage capacity of the battery before throwing it away.
The overall life of a rechargeable battery, however, is primarily dependent upon the number of and the efficiency of the charge cycles. Rechargeable batteries may be charged and reused after each discharge cycle. As with a primary battery, after a percentage of the battery storage capacity has been used, the battery typically cannot supply enough voltage to drive an electronic circuit. Thus, each discharge cycle of a rechargeable battery may be extended if a deeper discharge of the battery is provided. The level of discharge of a rechargeable battery, however, has an impact on the number of and the efficiency of future charges of the rechargeable battery. In general, as the depth of discharge of a rechargeable electrochemical cell increases, the number of charge cycles that a rechargeable electrochemical cell may undergo decreases. The optimal discharge characteristics of particular types of rechargeable electrochemical cells, however, vary widely. In a Nickel Cadmium (xe2x80x9cNiCdxe2x80x9d) battery, for example, a deep discharge is preferred because the battery may otherwise develop a xe2x80x9cmemoryxe2x80x9d effect if the battery is charged without being appropriately depleted resulting in a decreased capacity available for future charges. Deep discharge of a lithium battery, however, may damage the electrochemical cells. The service run time of a rechargeable electrochemical cell may generally be extended better by efficiently controlling the discharge and charge cycles of the particular cell such that the total number of charge cycles may be maximized and the amount of energy recovered from each discharge cycle of the electrochemical cell is also optimized.
In addition, consumers constantly demand smaller and lighter portable electronic devices. One of the primary obstacles to making these devices smaller and lighter is the size and weight of the batteries required to power the devices. In fact, as the electronic circuits get faster and more complex, they typically require even more current than they did before, and, therefore, the demands on the batteries are even greater. Consumers, however, will not accept more powerful and miniaturized devices if the increased functionality and speed requires them to replace or recharge the batteries much more frequently. Thus, in order to build faster and more complex electronic devices without decreasing their useful life, the electronic devices need to use the batteries more efficiently and/or the batteries themselves need to provide greater utilization of stored energy.
Some more expensive electronic devices include a voltage regulator circuit such as a switching converter (e.g., a DC/DC converter) in the devices for converting and/or stabilizing the output voltage of the battery. In these devices, multiple single-cell batteries are generally connected in series, and the total voltage of these batteries is converted into a voltage required by the load circuit by a converter. A converter can extend the run time of the battery by stepping down the battery output voltage in the initial portion of the battery discharge where the battery would otherwise supply more voltage, and therefore more power, than the load circuit requires, and/or by stepping up the battery output voltage in the latter portion of the battery discharge where the battery would otherwise be exhausted because the output voltage is less than the load circuit requires.
The approach of having the converter in the electronic device, however, has several drawbacks. First, the converters are relatively expensive to place in the electronic devices because every device manufacturer has specific circuit designs that are made in a relatively limited quantity and, thus, have a higher individual cost. Second, battery suppliers have no control over the type of converter that will be used with a particular battery. Therefore, the converters are not optimized for the specific electrochemical properties of each type of electrochemical cell. Third, different types of electrochemical cells such as alkaline and lithium cells have different electrochemical properties and nominal voltages and, therefore, cannot be readily interchanged. Additionally, the converters take up valuable space in the electronic devices. Also, some electronic devices may use linear regulators instead of more efficient switching converters such as a DC/DC converter. In addition, electronic devices containing switching converters may create electromagnetic interference (EMI) that may adversely affect adjacent circuitry in the electronic device such as a radio frequency (RF) transmitter. By placing the converter in the battery, however, the source of the EMI can be placed farther away from other EMI sensitive electronics and/or could be shielded by a conductive container of the battery.
Another problem with present voltage converters is that they typically need multiple electrochemical cells, especially with respect to alkaline, zinc-carbon, nickel cadmium (NiCd), nickel metal hydrate (NiMH), and silver oxide batteries, in order to provide enough voltage to drive the converter. In order to avoid this problem, present converters usually require multiple electrochemical cells connected in series to provide enough voltage to drive the converter, which may then step the voltage down to a level required by the electronic device. Thus, due to the converter""s input voltage requirements, the electronic device must contain several electrochemical cells, even though the electronic device itself may only require a single cell to operate. This results in wasted space and weight and prevents further miniaturization of the electronic devices.
Thus, a need exists to optimally use the stored charge of a rechargeable battery and optimize the depth of discharge before charging the battery in order to maximize its service run time. By designing batteries to provide a greater utilization of their stored energy, electronic devices can also use smaller or fewer batteries in order to further miniaturize portable electronic devices.
The present invention provides a battery that provides a longer service run time by optimally using the stored charge of a primary or a rechargeable battery before charging. The battery has a built-in controller that includes a converter, which may be capable of operating below the voltage threshold of typical electronic devices. The controller more efficiently regulates the voltage of the electrochemical cell and allows for a controlled discharge or an optimal discharge depth in order to extend the service run time of the battery. The controller is preferably disposed on a mixed-mode silicon chip that is custom designed for operation with a particular type of electrochemical cell such as an alkaline, nickel cadmium (xe2x80x9cNiCdxe2x80x9d), nickel metal hydrate (xe2x80x9cNiMHxe2x80x9d), lithium, lithium ion, sealed lead-acid (xe2x80x9cSLAxe2x80x9d), silver oxide or hybrid cell or with a particular electronic device.
The controller monitors and controls power delivery to the load to optimally extend the battery service run time by (1) turning on and off the DC/DC converter; (2) maintaining a minimum required output voltage when the input voltage is below that which typical electronic devices can operate; (3) lowering the battery output impedance; (4) determining the optimal discharge depth; (5) providing an optimal charge sequence; (6) increasing discharge current that given electrochemical cell can provide without controller; (7) providing high discharge current within cell safety limits even if this current exceeds converter maximum output current using by pass mode; (8) measuring remaining cell capacity; and (9) providing operating control signals to cell capacity indicators/xe2x80x98fuelxe2x80x99 gauges.
In a preferred embodiment, a single controller is mounted inside a housing of a multiple cell primary or rechargeable battery (e.g., a standard 9 volt battery). This aspect of the present invention provides several distinct advantages over placing the controller in the electronic device. First, it allows the battery designer to take advantage of particular electrochemical characteristics of a particular type of electrochemical cell. Second, if the device needs a converter only for a battery containing a particular type of electrochemical cell (e.g., lithium) to alter and/or stabilize the battery output voltage and not for a battery containing another type of electrochemical cell (e.g., NiCd, SLA), and the converter is integrated with the battery that requires the converter (i.e., the lithium battery), the electronic device may be designed without the DC/DC converter. This will allow for smaller circuit designs and prevent losses associated with the converter from affecting the battery that does not need the converter.
In a particularly preferred embodiment, the controller is mounted inside the container of a single-cell battery such as a AAA, AA, C, D or prismatic battery, or inside the container of each cell of a multiple-cell battery such as a prismatic or a standard 9 volt battery. This aspect of the present invention provides the advantages listed above for placing a single controller in a multiple-cell battery and provides even more advantages. First, it allows the controller to be custom matched to particular type of electrochemical cell to take advantage of its particular electrochemical reactions. Second, it allows for batteries having different types of electrochemical cells to be used interchangeably by either altering or stabilizing the output voltage or internal impedance to meet the requirements of electronic devices designed to operate on a standard battery. Both of these advantages, for example are met in a super efficient lithium cell that meets the packaging and electrical requirements of a standard 1.5 volt AA battery by using a built-in controller to step down the nominal cell voltage from the range from about 2.8 to about 4.0 volts to an output voltage of about 1.5 volts. By utilizing the higher cell voltage of a lithium cell, the designer can substantially increase the battery run time. Also, providing a controller in each battery cell provides a much more effective control over every cell than is presently available. The controller may monitor and control discharge conditions in each primary electrochemical cell and can ensure that each cell is completely exhausted before the electronic device shuts down. The controller may also monitor or control the discharge cycle in each rechargeable electrochemical cell to ensure that the cell is discharged to a level that will provide the longest possible service run time of the battery and will improve the safety of the cell to prevent conditions such as memory effects, short circuits or harmful deep discharges. The controller may also directly monitor and control the charge cycle of each rechargeable electrochemical cell that is in a battery to prevent conditions such as overcharging or short-circuiting to increase the cycle life and improve the safety of the battery. The charge state of single cells can also be signaled to consumers directly (visual, audio, vibration etc. indicators) or via xe2x80x98smartxe2x80x99 device interface.
The controllers also allow universal use of the batteries of the present invention. The batteries of the present invention provide advantages over known batteries regardless of whether they are used with electric, electromechanical, or electronic devices that have a cut-off voltage such as the ones listed above or with an electric device. In case of electrical, electromechanical, and electronic devices or appliances the batteries of present invention will maintain their peak performance until the very end of the batteries service run time. Utilizing controller with the battery the tail of the actual voltage versus time discharge curve could be profiled in such way so that it could emulate the typical discharge profile (without instantaneous end of service).
The controller chips can also be made much more economically because the large volume of battery sales allows for much less expensive production of the chips than individual regulator or converter designs can be made for each type of electronic device.
A preferred embodiment of the DC/DC converter is a high efficiency, ultra low input voltage, and medium power converter that utilizes a pulse-width, or -phase shift modulation, and pulse skip low duty control scheme with the start-stop oscillator control scheme.
Other features and advantages of the present invention are described with respect to the description of a preferred embodiment of the invention.